The present invention relates to a flat display device including means for scanning an electron beam over the image screen thereof, and particularly to such a device including a guide structure for confining and guiding the beam and for selectively extracting the beam from the guide.
Cathodoluminescent display devices which are presently used commercially, such as the display devices for television, generally include a neck and funnel extending perpendicularly from the screen and are thus relatively deep in the dimension perpendicular to the screen.
It has long been a desire to reduce the depth or thickness of such display devices to provide a substantially flat display device. As shown in U.S. Pat. No. 2,928,014 to W. R. Aiken et al, issued Mar. 8, 1960 entitled "Electronic Device Cathode Ray Tubes", one structure which has been proposed involves a guided beam approach which comprises a thin box-like envelope with one of the large surfaces thereof constituting a faceplate on which a phosphor screen is disposed. An electron gun is provided at one side of the screen, generally at one corner, and is arranged so as to direct a beam of electrons across the device in a path substantially parallel to the screen. Deflection elements are provided to selectively deflect the beam onto successive points of the screen to achieve the desired scanning thereof. The deflection elements are generally in the form of metal film electrodes coated on the back surface and on the sides of the tube.
In using the guided beam technique a problem has arisen in making flat display tubes having large area screens, such as screens which are about 30 inches by 40 inches. For such large size devices some type of internal support structure is required to prevent the evacuated envelope from collapsing. In a device having an internal support structure, the confinement and guiding of the electron beam is more critical than in a device which has no such supporting structure so as to prevent the supporting structure from interfering with the proper scanning of the beam along the screen. Also, in the guided beam flat display devices of the type shown in U.S. Pat. No. 2,928,014, high voltages have been needed to deflect the electron beam. It would be desirable to have such a display device which operates at lower voltages and still achieves satisfactory confinement and guidance of the beam.